Multi-scale (correlated quantum and statistical mechanics) modeling methods have been advanced and employed to guide the improvement of organic electro-optic (OEO) materials, including by analyzing electric field poling induced electro-optic activity in nanoscopic plasmonic-organic hybrid (POH) waveguide devices. The analysis of in-device electro-optic activity emphasizes the importance of considering both the details of intermolecular interactions within organic electro-optic materials and interactions at interfaces between OEO materials and device architectures. Dramatic improvement in electro-optic device performance--including voltage-length performance, bandwidth, energy efficiency, and lower optical losses have been realized. These improvements are critical to applications in telecommunications, computing, sensor technology, and metrology. Multi-scale modeling methods illustrate the complexity of improving the electro-optic activity of organic materials, including the necessity of considering the trade-off between improving poling-induced acentric order through chromophore modification and the reduction of chromophore number density associated with such modification. Computational simulations also emphasize the importance of developing chromophore modifications that serve multiple purposes including matrix hardening for enhanced thermal and photochemical stability, control of matrix dimensionality, influence on material viscoelasticity, improvement of chromophore molecular hyperpolarizability, control of material dielectric permittivity and index of refraction properties, and control of material conductance. Consideration of new device architectures is critical to the implementation of chipscale integration of electronics and photonics and achieving the high bandwidths for applications such as next generation (e.g., 5G) telecommunications.

Electrical resistivity, electron and hole barrier heights and interfaces can significantly affect the efficiency of electric field poling of non-linear optic (NLO) polymers. A combination of uniformity of the electric field distribution, charge carrier blocking and behavior of NLO chromophores can be optimized by introducing buffer layers and/or charge carrier blocking layers between the NLO polymer core layer and the anode and cathode electrodes, maximizing the poling field, chromophore alignment, nonlinearity or electro-optic (EO) coefficient, r33, and yield of the poled NLO polymers.

Taken together, theory-guided nano-engineering of organic electro-optic materials and hybrid device architectures have permitted dramatic improvement of the performance of electro-optic devices. For example, the voltage-length product has been improved by nearly a factor of 104 , bandwidths have been extended to nearly 200 GHz, device footprints reduced to less than 200 μm2 , and femtojoule energy efficiency achieved. This presentation discusses the utilization of new coarse-grained theoretical methods and advanced quantum mechanical methods to quantitatively simulate the physical properties of new classes of organic electro-optic materials and to evaluate their performance in nanoscopic device architectures, accounting for the effect on chromophore ordering at interfaces in nanoscopic waveguides.

In our previous work we introduced charge carrier blocking layers to realize an increase in the poling field and, hence, an increase in the nonlinearity, or electro-optic (EO) coefficient, r33, of the nonlinear optic (NLO) polymer disperse red 1:polymethylmethacrylate (DR1:PMMA). In addition, we not only achieved higher poling voltages, which resulted in higher r33s at these higher poling voltages, but we also observed higher r33s when both the samples with and without the charge carrier blocking layers were poled at the same poling voltage. We attributed that primarily to a decrease in the surface resistance. Here we provide a more detailed analysis and propose that the increase may be attributed not only to surface resistance but a combination of lower surface resistance, more uniform electric field distribution and charge carrier blocking, provided by the charge carrier blocking layers.

Nanophotonic modulators and photodetectors are key building blocks for high-speed optical interconnects in datacom and telecom networks. Besides power efficiency and high electro-optic bandwidth, ultra-compact footprint and scalable co-integration with electronic circuitry are indispensable for highly scalable communication systems. In this paper, we give an overview on our recent progress in exploring nanophotonic modulators and photodetectors that combine the specific strengths of silicon photonic and plasmonic device concepts with hybrid integration approaches. Our work comprises electro-optic modulators that exploit silicon-organic hybrid (SOH) and plasmonic-organic hybrid (POH) integration to enable unprecedented energy efficiency and transmission speed, as well as waveguide-based plasmonic internal photo-emission detectors (PIPED) with record-high sensitivities and bandwidths.

In our previous work we demonstrated a 3X increase in the nonlinearity, or electro-optic (EO) coefficient of the nonlinear optic (NLO) polymer disperse red 1:Polymethylmethacrylate (DR1: PMMA) by introducing a thin guanine nucleobase interfacial buffer layer, deposited between the NLO polymer and the cathode and a thin bathocuproine (BCP) interfacial buffer layer, deposited between the NLO polymer and the anode, being poled at 100 V/μm. In addition, we observed a 40% increase in EO coefficient by depositing either a thin sol-gel derived titanium dioxide layer or a thin guanine layer on either the anode or cathode side of the structure, poling at 100 V/μm. This paper addresses our analysis of these differences and is based on surface resistance.

Here we demonstrate a 3X - 6X increase in the nonlinearity, or electro-optic (EO) coefficient, and a 40% - 85% increase in working device yield, of the nonlinear optic (NLO) polymer disperse red 1:polymethylmethacrylate (DR1:PMMA) by introducing a thin guanine nucleobase interfacial buffer layer, deposited between the NLO polymer and the cathode and a thin bathocuproine (BCP) interfacial buffer layer, deposited between the NLO polymer and the anode. This has the potential to realize significantly higher EO coefficients without the need to synthesize new NLO polymer materials, as well as an increase in device yield due to less failure during poling.

We demonstrate silicon-organic hybrid (SOH) modulators for generating advanced modulation formats at high data rates and with low energy consumption. SOH integration combines slot waveguides on conventional silicon-on-insulator substrates with highly efficient electro-optic materials. With this approach we generate 16QAM signals at symbol rates of 28 GBd and 40 GBd leading to gross data rates (net data rates) of up to 160 Gbit/s (133 Gbit/s) for a single polarization. This is the highest value achieved by a silicon-based modulator up to now. With a maximum symbol rate of 28 GBd, low drive voltages of only 0.6 Vpp are sufficient and result in a record-low energy consumption of only 19 fJ/bit. This is the lowest energy consumption that has so far been reported for a 16QAM modulator at 28 GBd.

Here we demonstrate a 40% increase in the nonlinearity, or electro-optic (EO) coefficient, of the nonlinear
optic (NLO) polymer SEO100 with the addition of a thin guanine nucleobase buffer layer deposited between the
NLO polymer and the cathode electrode. We suggest that the high lowest unoccupied molecular orbital of guanine
flattens the field distribution at the high injection barrier reducing leakage current during poling. This has the
potential to realize higher EO coefficients without the need to synthesize new NLO polymer materials, as well as an
increase in device yield due to less failure during poling.

High-speed optical interconnects rely on advanced wavelength-division multiplexing (WDM) schemes. However, while photonic-electronic interfaces can be efficiently realized on silicon-on-insulator chips, dense integration of the necessary light sources still represents a major challenge. Chip-scale frequency comb sources present an attractive alternative for providing a multitude of optical carriers for WDM transmission. In this paper, we give an overview of our recent progress towards terabit communications with chip-scale frequency comb sources. In a first set of experiments, we demonstrate frequency comb generation based on silicon-organic hybrid (SOH) electro-optic modulators, enabling line rates up to 1.152 Tbit/s. In a second set of experiments, we use injection locking of a gain-switched laser diode to enerate frequency combs. This approach leads to line rates of more than 2 Tbit/s. A third set of experiments is finally dedicated to using Kerr nonlinearities in integrated nonlinear microcavities for frequency comb generation. We demonstrate coherent communication using Kerr frequency comb sources, thereby achieving line rates up to 1.44 Tbit/s. Our experiments show that frequency comb generation in chip-scale devices represents a viable approach to terabit communications.

Alignment of dipolar chromophores lies at the heart of organic electro-optic materials research. Among all the factors (e.g., external electric field, temperature, conductivity, etc.) affecting alignment efficiency or order parameter, interchromophore electrostatic interaction has been the focus of attention in the last decade. The strength of dipole interaction is highly dependent not only on dipole moment but also on chromophore shape and chromophore number density. Antiparallel interaction is dominant in the solid state of conventional EO chromophores (long and flat) and prevents electro-optic coefficient (r33) from scaling with chromophore concentration. Despite the great amount of research along various approaches to enhancing alignment, order parameters of organic EO materials are still low (0.13- 0.2 v.s. 1 for a perfect alignment). Antiparallel interaction can be selectively attenuated by attaching bulky groups to the middle part of chromophore. However, it is synthetically challenging to provide sufficient steric protection without causing severe reduction of chromophore concentration. In this paper, we will present the first realization of atomeconomic steric protection of chromophore against H-aggregation in all directions and show evidences for the dominance of head-tail interaction over antiparallel interaction of a highly dipolar chromophore. With the novel shape, the EO coefficients of guest-host films of the chromophore do not show attenuation with increasing concentration up to 100 wt%. The dominance of head-tail interaction also enabled fabrication of optical quality thick films from the neat chromophore and allows poling induced alignment to retain at temperatures above the poling temperature – a phenomenon never observed for other chromophores.

Coarse-grained Monte Carlo/molecular dynamic calculations are employed to explore the effect of various of
intermolecular electrostatic interactions upon chromophore order, lattice dimensionality, and viscoelasticity in
electrically-poled organic second order nonlinear optical materials. The following classes of organic macromolecular materials are considered: (1) Chromophore-polymer composites, (2) chromophores covalently incorporated into polymers and dendrimers, (3) chromophores incorporating additional dipolar or quadrupolar interactions that enhance poling efficiency, and (4) binary chromophore materials. For chromophore-polymer composites, the competition of chromophore-chromophore dipolar interactions and nuclear repulsive (steric) interactions define poling-induced acentric order. For covalently incorporated chromophores, covalent bond potentials also influence poling-induced order. These first two classes of materials basically behave as Langevin (3-D) lattice materials. Dipolar (e.g., coumarin) and quadrupolar (arene-perfluoroarene) interactions act to influence lattice dimensionality and thus enhance poling efficiency (the ratio of electro-optic activity to electric poling field strength). The long-range molecular cooperativity associated with these interactions influences viscoelastic properties critical to material processing and integration into silicon photonic, plasmonic, and metamaterial devices. The interaction between different chromophore species in binary chromophore materials also enhances poling efficiency. Polarized laser radiation applied to certain binary chromophore materials can also be used to enhance poling efficiency through control of lattice dimensionality. Poling efficiency approaching 5 (nm/V)2 has been achieved for these latter two classes of materials. Improvement in poling efficiency and control of material viscosity is particular important for integration of organic materials into complex device structures.

Optical phased arrays are promising candidates for both RF signal processing and optical beam forming and steering.
These platforms not only enable accurate electrically controlled beam steering at high frequencies but also have the
potential to significantly improve the performance of future free-space optical communications systems. In this work we
exploit recent advancements in both nano-scale hybrid silicon-slot waveguides and electro-optic (EO) polymers to
demonstrate an integrated optical phased-array antenna. Specifically, we create a hybrid integrated "photonic circuit"
that connects an array of optical phase modulators, fed by a common optical signal and a 1x4 splitter, to a compact
optical waveguide diffraction array for optical beam steering applications. The fundamental characteristics of the
resulting integrated optical beam former, including the optical insertion loss, driving voltage, and phase control from the
waveguide aperture are summarized in this letter.

Specific spatially-anisotropic interactions are identified that enhance noncentrosymmetric order required for electro-optic
activity. Enhancement of electric-field-poling-induced noncentrosymmetric order by these specific interactions is
shown to result from a reduction of lattice dimensionality from three to two dimensions. New analytical techniques for
measurement of centrosymmetric and noncentrosymmetric order and lattice dimensionality are introduced.
Measurement of order parameters is correlated with viscoelastic data to gain further insight into the influence of specific
interactions on poling efficiency and thus material electro-optic activity. The integration of organic electro-optic
materials into silicon photonic, plasmonic, and metamaterial devices is also discussed. These device structures can
affect the "effective" optical nonlinearity of organic materials but care must be exercised to control optical loss.

Passive and tunable optical filters as well as optical modulators, directly fabricated on the end-faces of optical fibers can
provide a fast and low cost production. A hybrid layer system can be built up to a passive Fabry-Pérot microcavity,
where alternating dielectric high and low refractive materials are used as mirrors and a highly transparent polymer as the
spacer material. The mirror design and the spacer thickness define the center operation wavelength and the filter
bandwidth. Bandwidths of less than 1 nm (FWHM) at a wavelength of 1560 nm could be achieved for such microcavities
on the end-faces of optical fibers.
Enhancing the hybrid layer system by transparent conductive electrodes and by adding electro-optically active
chromophores to the polymeric spacer material, the filters become tunable. The material used for the electrodes is indium
tin oxide (ITO). The oxidic electrodes have to be merged with the dielectric mirrors and the polymeric spacer. Applying
a voltage to the electro-optically active polymeric spacer utilizing such electrodes, the refractive index of the spacer can
be changed and therefore the resonance criteria of the microcavity.

This communication focuses on the integration of organic nonlinear optical and gain materials into plasmonic and
metamaterial device architectures and most specifically focuses on the integration of organic electro-optic (OEO)
materials into such structures. The central focus is on structures that lead to sub-optical wavelength concentration of
light (mode confinement) and the interaction of photonic and plasmonic modes. Optical loss and bandwidth limitations
are serious issues with such structures and optical loss is evaluated for prototype device architectures associated with the
use of silver and gold nanoparticles and membranes supporting plasmonic resonances. Electro-optic activity in organic
materials requires that chromophores exhibit finite noncentrosymmetric organization. Because of material conductivity
and integration issues, plasmonic and metamaterial device architectures are more challenging than conventional triple
stack all-organic device architectures and electro-optic of a given OEO material may be an order of magnitude less in
such structures. Because of this, we have turned to a variety of materials processing options for such integration
including crystal growth, sequential synthesis/self assembly, and electric field poling of materials deposited from
solution or by vapor deposition. Recent demonstration of integration of silicon photonic modulator and lithium niobate
modulator structures with metallic plasmonic structures represent a severe challenge for organic electro-optic material
plasmonic devices as these devices afford high bandwidth operation and attractive VμL performance. Optical loss
remains a challenge for all structures.

Theoretical calculations have demonstrated that the ratio of second and third degree order parameters can define lattice
dimensionality and furthermore, that an increased ratio of second to third degree order parameters represents reduced
lattice dimensionality. As a result, the third degree order parameter (i.e. acentric order parameter) is increased, causing
an increase in electro-optic activity with reduced lattice dimensionality. Experimentally, specific spatially-anisotropic
interactions associated with coumarin moieties and Frechet-type (arene/perfluoroarene) dendrons have been incorporated
into chromophore systems and have been shown to lead to lattices of reduced dimensionality, resulting in increased
values of the acentric order parameter and therefore, electro-optic activity. Reductions in lattice dimensionality can also
arise from guest chromophore-host chromophore interactions in binary chromophore organic glasses and from laserinduced
ordering of host lattice chromophores observed in the laser-assisted electric field poling of azo-dye-containing
host lattices. These interactions in various chromophore systems including investigation of EO and order properties are
discussed.

Theoretically-inspired design of new organic electro-optic materials has resulted in dramatic improvement in electrooptic
activity at telecommunication wavelengths to values of approximately 600 pm/V. In particular, a new class of
materials, binary chromophore organic glasses, has been introduced, which afford attractive linear and nonlinear optical
properties. The intermolecular electrostatic interactions among guest and host chromophores in these new materials
augment the induction of noncentrosymmetric order by an electric poling field or by laser-assisted electric field poling.
Another important advance in the utilization of organic electro-optic materials has been the incorporation of these
materials into 25-150 nm slots in silicon photonic waveguides. The concentration of optical and electrical fields in these
nanoscopic device structures dramatically reduces drive voltage requirements.

Photonic technologies hold the promise of transformative advances in the telecommunications, aerospace, and
computing industries. In particular, organic materials displaying electro-optic coefficients an order of magnitude larger
than the current industry standard inorganic materials (r33 ≥ 300 pm/V) may hold the key to the development of cheap,
high bandwidth, and highly integratable electro-optic devices. The pertinent linear and nonlinear optical properties of
such organic second-order nonlinear optical materials are highly dependant on their dielectric properties as well as the
extent of dipolar order that can be created. Here, theoretical approaches to the simulation of highly active organic
electro-optic materials are described. Such simulations assist understanding and may be used to predict optical properties
facilitating the rational design process. Improved ordering schemes, such as laser-assisted electric-field-poling may help
in the translation of large chromophore hyperpolarizability values into large r33. Recent results also suggest that
incorporation of these improved organic materials into new hybrid organic/silicon device designs may lead to
dramatically reduced device operational voltages and create opportunities for the development of new device
functionality.

The effects of surface scattering on terahertz reflection spectrum for explosive detection are studied by measuring
terahertz reflection pulses from sandpapers with different roughness coated with gold. The experimental results show that
the amplitude decrease and pulse broadening of the detected signal caused by the surface scattering result in the width
reduction of Gaussian distribution of the specular scattering coefficient spectrum. A simple analytical model is applied to
the analysis of experimental results and good agreements are obtained.

Polymers that contain conjugated molecules can change their index of refraction upon bonding with high
explosive molecules. These polymers can be incorporated into micro-ring resonators as trace explosive sensor. Since
the resonator cavity itself is made of sensing material, the detection is intrinsic, which may lead to higher sensitivity
and faster response than other fiber optic chemical sensors. Photobleaching was used for the fabrication of the
microrings resonators. The sensor has shown ppb level of sensitivity to the vapor of an explosive stimulant 2,4-
dinitrotoluene and is insensitive to common chemical pollutants including nitrates, sulfates and phosphates.

A major breakthrough in the area of organic electro-optic (EO) materials has been recently achieved. To go beyond the
oriented gas model limit for organic EO materials, new approaches of using nanoscale architecture control and
supramolecular self-assembly have been proved as a very effective method to create a new paradigm for materials with
very exciting properties. High-performance EO polymers were demonstrated by a facile and reliable Diels-Alder "click"
reaction for postfunctionalization and lattice hardening to improve EO activity and thermal stability. This type of "click"
chemistry paves the way to systematically study the relationship among EO activity, chromophore shape, and number
density of the chromophores. Reversible supramolecular interactions were also introduced to a new generation of EO
dendrimers and polymers to create self-assembled nano-objects, overcome strong intermolecular electrostatic
interaction, and improve their poling efficiency and stability. These self-organized EO materials were used as hosts in a
binary chromophore system to further improve chromophore number density and r33 value. With these novel approaches,
we succeeded in enlarging the full potential of organic NLO materials by a factor of 3~5 and developing a variety of
nano-structured organic EO materials with ultrahigh r33 values (>300 pm/V at the wavelengths of 1310 and 1550 nm,
more than 10 times that of LiNbO3) and excellent auxiliary property, such as thermal stability and optical transparency.
The success of these material developments has inspired the exploration of new device concepts to take full advantage of
organic EO materials with ultrahigh r33 values.

Photobleaching was used for the fabrication of electro-optic polymer microrings resonators. All the device
parameters were theoretically optimized. The photobleaching mask was made using e-beam lithography. UV exposure
through the mask defined the pattern in the polymer by an irreversible change of the material properties and decrease of
the refractive index. Waveguide coupled microring resonators have shown 15 dB resonance contrast and low total
insertion loss of 9 dB, most of which was mainly due to fiber coupling in and out of the chip.

Chromophore-polymer composite materials for electro-optical applications are rendered active at the χ(2) level
of susceptibility by inducing chromophore alignment through the interaction of the chromophore dipole moment with an
external electric field, a process referred to as "poling". To provide insight into the molecular details of the poling
process, single molecule microscopy studies of DCM (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4Hpyran)
and RhB (Rhodamine B) in poly(methyl acrylate) (PMA) above Tg of the polymer host are performed. Electric
fields of 50 V/μm are employed consistent with typical experimental conditions. The effect of environment is studied
through comparative studies or RhB reorientation in oxidative and inert atmospheres. Single-molecule rotational
dynamics are monitored through the time-evolution of the fluorescence anisotropy. Anisotropy correlation functions
demonstrate non-exponential decay consistent with previous studies of molecular rotation dynamics in polymer melts.
The rotational dynamics of DCM are found to be weakly perturbed in the presence of a 50 V/μm electric field consistent
with the modest alignment potential created by the electric field relative to the amount of available thermal energy. The
relevance of these findings to current models of the poling process is discussed.

The macroscopic electro-optic activity of organic materials is linearly related to molecular first hyperpolarizability of individual chromophores, chromophore number density, and the acentric order parameter describing chromophore order. When strong chromophore-chromophore intermolecular electrostatic interactions (e.g., dipole-dipole interactions) are present, the latter two quantities are not independent. In previous publications, we have demonstrated how electro-optic activity can be systematically improved by control of chromophore shape in chromophore/polymer composite materials and by the nanoscopic engineering of single- and multi-chromophore-containing dendrimer materials, where steric interactions and covalent bond potentials are used to inhibit centrosymmetric ordering of chromophores. In this communication, we demonstrate how doping a second chromophore into a chromophore-containing material can lead to dramatically improved electro-optic activity. This work also provides insight into the affect of surrounding lattice on solvatochromic shifts and line broadening that can lead to increased optical loss.

Conjugated chromophores with permanent dipole moments can be aligned by heating a thin polymer film containing chromophores in an external electric field. The heated "guest-host" system is then cooled in the field to maintain the chromophores' alignment. Dielectric breakdown and charge transfer, however, often limit the external electric field to about 100 V/μm of film thickness. It was hypothesized that electrical pulses could increase the voltage of the poling field without damaging the sample films. This was achieved by combining an amplified waveform from a function generator with the DC poling field. Pulse amplitudes were varied from 10 to 103 V. Pulse frequencies were varied from 10-1 to 103 Hz with a duty cycle of up to 50% of the pulse period. Pulse amplitudes were found to have optimum effects at less than 15% of the DC field at low frequencies, 0.1-10 Hz, with a sinusoidal pulse shape. It was found that this technique induced up to a 20% improvement in optical properties without damaging the sample films.

A novel broadband E-field sensor based on electro-optic polymer micro-ring resonator directly coupled to the core of optical fiber is proposed and demonstrated. A flat is made on the side of the optical fiber by polishing and an electro-optic polymer waveguide in the shape of a ring is placed on the polished flat. One side of the ring is directly above the core of the fiber and light is evanescently coupled between the fiber and the micro-ring. External electric fields change the index of refraction of the ring resonator and therefore its resonant wavelengths. The sensor is all dielectric without metal layers to distort the measured E-field. The resonance structure allows the sensor to potentially have much higher sensitivity than other electro-optic sensors based on interferometry or polarization modulation. Since electro-optic polymers have higher electro-optic coefficients, lower dielectric constants and faster electro-optic responses than inorganic crystals, higher sensitivity, lower invasiveness and higher bandwidth of E-field sensing can be expected. The sensor with EO polymer micro-ring directly coupled to side-polished fiber eliminates unreliable and possibly lossy fiber to waveguide butt coupling as well as the high propagation loss which comes from the long straight EO polymer waveguides. Unlike devices based on waveguide technology, a supporting substrate is not necessary in this device. This leads to sensors of small size and low disturbance to the measured electric field. In the proof-of-concept experiment, a sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system) using
AJLS103 electro-optic polymer.

Recently developed organic electro-optic materials have demonstrated large increases in activity creating a drive towards utilizing organics in ring micro-resonators and modulators. These materials allow for extremely low drive voltages and fundamental response times within the terahertz region. Present synthetic efforts have efficiently incorporated molecules with large first molecular hyperpolarizabilities, β, into macromolecular systems producing unprecedented electro-optic coefficients, r33. Previously, incorporation of these large β molecules into macromolecular systems proved difficult due to phase separation or molecular aggregation within the processed films. Therefore, integration into workable devices was inconsistent and difficult. The new material systems however, have shown considerably enhanced film qualities, leading to improved device incorporation and fabrication. This paper will focus on current organic materials strategies and their incorporation into current ring micro-resonator devices and results.

In EO polymer materials, the second-order nonlinear optic chromophores must be oriented in one direction in order to be electro-optically active. Interchromophore electrostatic interactions, which encourages the formation of non-active and light-scattering crystalline domains through the antiparallel stacking of dipoles, have long been an obstacle to the translation of large molecular optical nonlinearity into corresponding bulk nonlinearity. Great progresses have been made in the design and synthesis of chormophores with reduced electrostatic interactions. New effort toward the complete elimination of the destructive effect of the electrostatic forces is on the way. On the contrary, strong intermolecular electrostatic interaction (e.g. the force responsible for π-π stacking of conjugated systems) is often desired in LED, transistor and photovoltaic (PV) devices since high mobilities of the charge carriers are the key to their high performances and often come from ordered stacking of pi-conjugated systems. For PV applications, bi-continuous "bulk heterojunction" of electron donor (D) and acceptor (A) is ideal for efficient charge carrier generation, transport and collection. Differential electrostatic interactions between D and A is the key to the formation of such morphology. We have synthesized a novel type of block copolymer having a basic unit of D-B-A (B is a non-conjugate bridge) for solar cell application. D and A can be designed in such a way that D-D and A-A interactions are stronger than the D-A interaction, and therefore, have a strong tendency to phase separate.

The motivation for use of organic electro-optic materials derives from (1) the inherently fast (sub-picosecond) response of π-electron systems in these materials to electrical perturbation making possible device applications with gigahertz and terahertz bandwidths, (2) the potential for exceptionally large (e.g., 1000 pm/V) electro-optic coefficients that would make possible devices operating with millivolt drive voltages, (3) light weight, which is a concern for satellite applications, and (4) versatile processability that permits rapid fabrication of a wide variety of devices including conformal and flexible devices, three dimensional active optical circuitry, hybrid organic/silicon photonic circuitry, and optical circuitry directly integrated with semiconductor VLSI electronics. The most significant concerns associated with the use of organic electro-optic materials relate to thermal and photochemical stability, although materials with glass transition temperatures on the order of 200°C have been demonstrated and photostability necessary for long term operation at telecommunication power levels has been realized. This communication focuses on explaining the theoretical paradigms that have permitted electro-optic coefficients greater than 300 pm/V (at telecommunication wavelengths) to be achieved and on explaining likely improvements in electro-optic activity that will be realized in the next 1-2 years. Systematic modifications of materials to improve thermal and photochemical stability are also discussed.

This communication primarily deals with utilizing organic electro-optic (OEO) materials for the fabrication of active wavelength division multiplexing (WDM) transmitter/receiver systems and reconfigurable optical add/drop multiplexers (ROADMs), including the fabrication of hybrid OEO/silicon photonic devices. Fabrication is carried out by a variety of techniques including soft and nanoimprint lithography. The production of conformal and flexible ring microresonator devices is also discussed. The fabrication of passive devices is also briefly reviewed. Critical to the realization of improved performance for devices fabricated from OEO materials has been the improvement of electro-optic activity to values of 300 pm/V (or greater) at telecommunication wavelengths. This improvement in materials has been realized exploiting a theoretically-inspired (quantum and statistical mechanics) paradigm for the design of chromophores with dramatically improved molecular first hyperpolarizability and that exhibit intermolecular electrostatic interactions that promote self-assembly, under the influence of an electric poling field, into noncentrosymmetric macroscopic lattices. New design paradigms have also been developed for improving the glass transition of these materials, which is critical for thermal and photochemical stability and for optimizing processing protocols such as nanoimprint lithography. Ring microresonator devices discussed in this communication were initially fabricated using chromophore guest/polymer host materials characterized by electro-optic coefficients on the order of 50 pm/V (at telecommunication wavelengths). Voltage-controlled optical tuning of the pass band of these ring microresonators was experimental determined to lie in the range 1-10 GHz/V or all-organic and for OEO/silicon photonic devices. With new materials, values approaching 50 GHz/V should be possible. Values as high as 300 GHz/V may ultimately be achievable.

Quantum and statistical mechanical calculations have been used to guide the improvement of the macroscopic electro-optic activity of organic thin film materials to values greater than 300 pm/V at telecommunication wavelengths. Various quantum mechanical methods (Hartree-Fock, INDO, and density functional theory) have been benchmarked and shown to be reliable for estimating trends in molecular first hyperpolarizability, β, for simple variation of donor, bridge, and acceptor structures of charge-transfer (dipolar) chromophores. β values have been increased significantly over the past five years and quantum mechanical calculations suggest that they can be further significantly improved. Statistical mechanical calculations, including pseudo-atomistic Monte Carlo calculations, have guided the design of the super/supramolecular structures of chromophores so that they assemble, under the influence of electric field poling, into macroscopic lattices with high degrees of acentric order. Indeed, during the past year, chromophores doped into single- and multi-chromophore-containing dendrimer materials to form binary glasses have yielded thin films that exhibit electro-optic activities at telecommunication wavelengths of greater than 300 pm/V. Such materials may be viewed as intermediate between chromophore/polymer composites and crystalline organic chromophore materials. Theory suggests that further improvements of electro-optic activity are possible. Auxiliary properties of these materials, including optical loss, thermal and photochemical stability, and processability are discussed. Such organic electro-optic materials have been incorporated into silicon photonic circuitry for active wavelength division multiplexing, reconfigurable optical add/drop multiplexing, and high bandwidth optical rectification. A variety of all-organic devices, including stripline, cascaded prism, Fabry-Perot etalon, and ring microresonator devices, have been fabricated and evaluated.

Theoretical guidance, provided by quantum and statistical mechanical calculations, has aided the recent realization of electro-optic coefficients of greater than 300 pm/V (at 1.3 microns wavelength). This articles attempts to provide physical insight into those recent results and to explore avenues for the further improvement of electro-optic activity by structural modification, including to values of 500 pm/V and beyond. While large electro-optic coefficients are a necessary condition for extensive practical application of organic electro-optic materials, they are not a sufficient condition. Adequate thermal and photochemical stability, modest to low optical loss, and processability are important additional requirements. This article also examines such properties and suggests routes to achieving improved auxiliary properties.

Hyper-Rayleigh scattering (HRS) is used to measure the first-hyperpolarizability (β) of electro-optic (EO) chromophores. One of the inherent concerns in any HRS measurement is the extent to which resonant enhancement contributes to the observed intensity thereby leading to inaccuracies when evaluating chromophore potential for application in electro-optical devices. One way to address this concern is to employ increasingly longer excitation wavelengths far from resonance. However, in charge-transfer-based non-linear optical chromophores, enhanced β generally correlates with a red-shift of the charge transfer absorption band so that even at the longest excitation wavelengths generally employed in HRS studies, resonant enhancement remains an issue. We have adopted an alternative approach in which the wavelength dispersion of the HRS intensity is determined by performing measurements at a variety of excitation wavelengths. This approach allows one to ascertain the role of resonance enhancement thereby allowing for more accurate correlation of improved β with molecular architecture. We report the results of our HRS studies for nine chromophores employing excitation wavelengths ranging from 780 to 1907 nm. Our HRS results demonstrate good agreement with the predictions of density functional theory. This synthesis of experimental and theoretical techniques has resulted in more effective designs for the next generations of electro-optical chromophores.

A novel wavelength selective 2x2 switch based on two microring resonators is proposed. The device consists of two intersecting channel waveguides with each of the two rings coupled to both waveguides. Depending on the control voltage the light of selected wavelength either can propagate through the straight waveguide or can be coupled to one of the rings and from the ring couple to the perpendicular output. Therefore every ring can independently switch one wavelength from any input to the perpendicular output. This wavelength selective switching adds to the traditional switch functionality. Theoretical calculations were carried out to determine optimum parameters of the switch and soft-lithography was used for implementation. Being fabricated from the latest electro-optical polymers this device can provide very high switching speed and low operation voltage.

Recent breakthroughs in developing exceptional organic electro-optic (EO) materials are reviewed. Whole series of guest-host polymers furnished with high μβ chromophores have shown large electro-optic coefficients around 100~160 pm/V @ 1.31μm. Moreover, new generation of NLO chromophores based on pyrroline and pyrrolizine acceptors have been designed and synthesized. To go beyond the typical oriented gas model limit for poled polymers, new approach of
using nanoscale architecture control and supramoleaular self-assembly has been proved as a very effective method to create a new paradigm for materials with very exciting properties. The approaches of employing Diels-Alder reactions for postfunctionalization and lattice hardening also provide a facile and reliable way to generate high-performance EO polymers and dendrimers. This type of "click" chemistry paves the way to systematically study the relationships between chromophore shape and number density, controlled self-assembly, in addition to provide the material properties needed for multi-layer device fabrication. Finally, a new generation of binary monolithic glasses has been developed that exhibit unprecedented high EO activities through careful manipulation of intricate supramolecular interactive forces for self-assembly. The results obtained from these poled binary organic glass materials (r33 as high as 310 pm/V at 1.31μm) are the highest values ever reported which are >10 times of the commercial lithium niobate crystals. The success of these material developments has recently inspired the exploration of new device concepts trying to take full advantage of the organic EO materials with ultrahigh r33 values.

Organic electro-optic materials offer exceptional processability (both from solution and the gas phase) that permit fabrication of flexible and conformal device structures and the integration of organic materials with a wide range of disparate materials. In addition, organic electro-optical materials have fundamental response times that are in the terahertz region, and useable electro-optic coefficients that are approaching 300 pm/V (at telecommunication wavelengths). In addition to fabrication by traditional lithographic methods, multiple devices on a single wafer have been fabricated by soft and nano-imprint lithography. In this presentation, we review the fabrication and performance evaluation of a number of all-organic and organic-silicon photonic ring microresonator devices. Both electrical and thermal tuning of devices, including both single and multiple ring micro-resonators, are demonstrated.

We have developed a novel approach for fabricating and testing optical ring resonators. Using a side-polished optical fiber and fabricating a ring waveguide directly over its core, an efficient and passive signal filter in the 1.55 um telecommunication band is created. A standard single mode optical fiber is permanently secured in an arcing groove in quartz and is side polished proximally to its core. The ring resonator is fabricated using two-photon initiated free-radical polymerization of tri-functional acrylate on low-index quartz substrate with a 100 femtosecond pulsed Ti/sapphire laser. The quartz substrate is inverted and vacuum mounted to an X-Y-Z stage so that the polymer ring waveguide can be positioned directly above the core of the fiber forming a vertically coupled ring resonator. Our technique allows infinite variation of the width, height, diameter and location (therefore the coupling strength between the fiber and the ring) of the ring resonator waveguide. This approach enables resonators to be fabricated, tested and subsequently removed multiple times on the same side-polished fiber, refining both the ring resonator geometry and materials. Because it is a fiber-based device, it possesses negligibly low optical insertion loss and can be used for fixed and tunable wavelength filters, intensity modulators, and fiber-optic sensors. Both theoretical analysis and experimental data will be presented.

In this paper, we report a novel technique that combines push-pull Mach-Zehnder modulator structure with dc bias to achieve fractional volt half-wave voltage in intensity modulation. The technique is accomplished by simultaneously applying a common mode operation voltage and a differential dc bias voltage on the two arms of a Mach-Zehnder modulator. The modulators are tested for half-wave voltage at different temperatures while applying different push-pull biases. The results are compared with a push-pull EO polymer modulator that has identical dimensions and the same materials, and which is fabricated and poled with conventional method. It is found that our new approach reduces the half-wave voltage by a factor of more than five.

Organic materials have great potential for electro-optic devices. Achieving higher unidirectional ordering of chromophores is the main challenge in using organic materials in such devices. The prime reason for this decreased order is due to interchromophore interactions which lead to a decrease in the electro-optic coefficient, r33. A material consisting of a chromophore surrounded by dendrons and possessing an appropriate aspect ratio should facilitate the near Ferro-electric ordering as observed in the discotic liquid crystals. For that purpose, a prototype dendrimeric chromophore has been synthesized and will be used in Mach-Zehnder devices to achieve lower drive voltages.

The procedure for increasing the temperature and electric field to set poling conditions for guest-host nonlinear optic polymers was evaluated. Specifically, the order of the two variables was alternated and the poling efficiency was evaluated by comparing the electro-optic coefficient, r33 for both procedures. Two host polymers, poly(methyl)methacrylate (PMMA) and poly[bisphenol A carbonate-co-4,4'(3,3,5-triethyl cyclohexylidene) diphenol] (APC) were doped with 10% (by weight) of the chromophore disperse red 1 (DR1). Single layer films were spin deposited onto a glass substrate with patterned indium tin oxide (ITO) as the bottom electrode and patterned gold as the top electrode. With the final set poling temperature and electric field held constant, each system was poled under two different poling procedures. The first procedure was to increase the temperature at a constant rate first and then increase the electric field at a constant rate to the final set poling conditions, and conversely, the second procedure was to increase the electric field at a constant rate, at room temperature, first and then increase the temperature at a constant rate to the final set poling conditions. An increase in poling efficiency was found for the 'Voltage then Temperature' procedure in both guest-host systems with an increase in r33 values of 38% to 43%. While this dramatic increase is not expected for every system, it shows that there is an additional variable of poling procedure that can be modified for enhancing the efficiency of poling.

Systematic development of electro-optic (EO) polymers is leading to optical and material properties such that they present an increasingly viable alternative to crystalline-based technologies for integrated optics. EO polymers demonstrate an inherent velocity match between radio-frequency and optical waves, making them excellent candidates for applications in high-speed telecommunication switching and optical interconnects for VLSI circuitry. In addition, EO polymer devices are relatively simple to fabricate at conditions compatible with microelectronics industry processes, making same-substrate integration of optical and electronic circuitry possible. In this paper, we describe two vertical integration schemes whereby a polymer-based electro-optic modulator may be controlled by metal-oxide semiconductor field effect transistor (MOSFET) circuitry. One scheme described is an insitu integration on the same silicon (Si) substrate. The second scheme is the integration of a modulator built on a flexible substrate with a MOSFET circuit on a second Si substrate. Both schemes have potential applications for integrated electro-optics.

Future generations of flexible, transparent electronics will require the use of polymer based thin-film transistors (TFTs) exhibiting high carrier mobility. The problem of enhancing TFT characteristics is addressed in this report. We investigate the nanoscale, self-assembled monolayer (SAM) influence on organic-based thin film transistors (OTFT) at the interface between semiconducting polymer and both the source/drain metal contacts and the insulator. Capacitance-voltage (C-V) characteristics help to elucidate the role of SAMs in the OTFT structure and the charge injection mechanism. Positive trends and parasitic effects are also addressed in characterization.

The potential of organic electro-optic materials for large electro-optic activity and fast response to applied electric fields (leading to 100 GHz device bandwidths) is important and increasingly well-recognized. In this communication, we demonstrate how quantum and statistical mechanical calculations can be used to guide the systematic improvement of both molecular first hyperpolarizability (β) and macroscopic electro-optic activity (r). Femtosecond time-resolved, wavelength-agile Hyper-Rayleigh Scattering (HRS) measurements have been used to measure β values relative to chloroform and to avoid confusion associated with two photon contributions. Electro-optic coefficients have been characterized by simple reflection (Teng-Man method), attenuated total reflection (ATR), and Mach Zehnder interferometry. "Constant bias" modifications of these techniques have been used to permit investigation of optimized poling conditions. Organic electro-optic materials also afford unique advantages for the fabrication of conformal and flexible devices, for the integration of disparate materials, and for exploitation of novel manufacturing technologies such as soft lithography. Both stripline and ring microresonator structures have been fabricated by soft lithography. The integration of organic electro-optic materials with silicon photonics (both split ring microresonators and photonic bandgap circuitry) has been demonstrated.

Deoxyribonucleic Acid (DNA) extracted and purified from salmon sperm was investigated for use in electro-optic devices as a cladding layer. The 500,000 molecular weight material has a refractive index less than that of common core materials such as poly(methyl)methacrylate (PMMA) and amorphous polycarbonates, shows a resistivity two orders of magnitude lower than common core materials, and shows no signs of degradation within 100°C of the host poling temperature. DNA was analyzed as a cladding material for two different chromophore systems, Disperse Red 1 (DR1), and Cheng-Larry Dalton 1 (CLD1) in a PMMA guest/host system. A baseline device, comprised only of a 1.7μm layer of PMMA, was tested for non-linearity with each chromophore, with the r33 value increasing with increasing temperature and voltage. Doublestack devices included a 1μm thick DNA film as the cladding layer with the baseline core layer above. Based on the dielectric properties of DNA, values of r33 were calculated for the theoretical behavior of the devices. The recorded r33 values were accurate within 5% of the calculated values with the DR1 chromophore, and within 20% with the CLD1 chromophore, hence showing good device reproducibility.

Future generations of flexible, transparent electronics require the use of polymer based thin-film transistors (TFTs) with high carrier mobility. The problem of enhancing TFT characteristics is addressed in this report. Systematic studies were performed to optimize the thickness and composition of the active and dielectric layers. Different electrode materials were tested along with “top” and “bottom” device configurations. Various coating techniques (SAM) were applied to achieve a higher degree of order in polymer chains of semi-conducting layer. Results demonstrate the influence of the mentioned factors on the TFT performance, including increase of mobility and on/off ratio.

Recent use of quantum mechanics to guide the improvement of molecular hyperpolarizability and the use of statistical mechanical analysis of the effects of intermolecular electrostatic interactions to improve the acentric ordering of organic chromophores has led to the realization of electro-optic coefficients, r33, greater than 100 pm/V (at telecommunication wavelengths). This material design and development paradigm is likely to lead to further improvement in electro-optic activity, which will in turn facilitate the development of a variety of electro-optic devices with drive (Vπ) voltage requirements of less than one volt. The utility of organic electro-optic materials for development of high bandwidth devices is now well documented. What is less obvious is the utility of organic electro-optic materials for the fabrication of complex (including conformal, flexible, and three-dimensional) device structures. In this communication, we review recent improvements in electro-optic activity; thermal and photochemical stability; and processability of organic electro-optic materials and the use of these materials to fabricate conformal and flexible electro-optic devices and devices based upon single and multiple coupled ring microresonators.

Density functional theory calculations were used to develop understanding of the effects of differing substitution patterns in multiply donor and acceptor substituted nonlinear optical chromophores. A novel series type substitution design was presented and evaluated. Calculations were performed for a number of structures and hyperpolarizability values were compared. The data obtained showed an increase in molecular first hyperpoloarizability in multifunctional chromophores based on this series type design as compared with linear molecules constructed from the same donor-bridge-acceptor components. This data was then used to direct the synthesis of novel nonlinear optical chromophores.

Recent development of high-performance nonlinear optical polymers for electro-optics (E-O) is reviewed in this paper. A highly efficient and thermally stable nonlinear optical (NLO) chromophore, namely 2-[4-(2-{5-[2-(4-{Bis-(tert-butyl-dimethyl-silanyloxy)-ethyl]-amino}-phenyl)-vinyl]-thiophen-2-yl}-vinyl)-3-cyano-5-trifluoromethyl-5H-furan-2-ylidene]-malononitrile, has been prepared and incorporated in amorphous polycarbonate (APC) composites. The result from high electric field poling shows a very large E-O coefficient (r33 = 94 pm/V at 1.3 μm), ~80% of which can be maintained at 85 °C for more than 500 hours. In addition to this guest/host sysytem, a high Tg side-chain polymer, derived from a 3-D cardo-type polimide with dendron-encapsulated chromophores as pendent groups has also been synthesized and characterized. A high degree of chromophore dipole orientation and a large r33 of 71 pm/V at 1.3 μm can be achieved in this poled polyimide. More than 90% of its E-O activity can be maintained at 85 °C for more than 600 hours. To access the full potential of poled polymers for device applications, we have developed a new lattice-hardening approach to overcome the “nonlinearity-stability-tradeoff” of conventional thermoset methods. By using the Diels-Alder lattice-hardening process, we can achieve the same high poling efficiency and large r33value as in a guest-host system while maintaining good thermal stability seen in densely-crosslinked polymers. By modifying the electronic properties of the crosslinking reagents, we can fine-tune the processing temperature window of the Diels-Alder reactions to achieve hardened materials with optimal properties.

In pursuit of greater understanding of structure property relationships in NLO chromophores, a series of molecules consisting of three aromatic rings was synthesized. The relative positions of benzene and thiophene rings in these molecules were varied. Theoretical calculations also suggest that the use of a slightly electron deficient heteroaromatic, such as thiazole, can increase β through the concept of an electronic gradient. The use of this heteroaromatic in the correct orientation can compensate for the energetic barrier that benzene presents during charge-transfer. Hyper-Raleigh Scattering (HRS) measurements on three of these “gradient bridge” type chromophores show that benzene located at the donor end provided the highest hyperpolarizability. The poor solubility of these three-ring systems severely limited their processability and gave considerable synthetic challenges. The difference in theoretical and experimental trends of β are discussed.

There is a considerable interest in the use of metal centered materials as a light source in the growing field of organic light emitting devices (OLED's). In these devices, a polymeric host matrix containing either a carbazole type polymer or polyfluorene derivatives is used to help facilitate energy transfer to the luminophore. We have shown that by using a gadolinium complex that consist of three equivalents of a chelated dibenzoylmethane b-diketone ligand and one equivalent of a phenanthroline type ligand as a component in the host matrix, the performance of a double layer type OLED is improved. We have studied OLED systems that contain tris chelated europium compounds that contain three equivalents of partially fluorinated β-diketone type ligands and an equivalent of a phenanthroline type ligand. In these devices, the external efficiency has shown a 30-fold increase. We have also shown there is an increase for Osmium based OLED's that use the gadolinium complex as part of the polymer matrix. In these devices, the maximum quantum efficiency increased from 2.1% to a value of 3.8%.

Electrophosphorescence tuned from the green to red (522 nm - 650 nm) was achieved from double-layer light emittng devices using osmium (Os) complexes doped blend of either poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD), or poly(vinyl naphthalene) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVN:PBD) as the emitting layer. Blending PVN with PBD greatly suppresses the electromer emission of PVN. The PVN:PBD blend emanates a short wavelength EL emission peaking at around 375 nm, which well overlaps with the absorption spectra of the Os complexes and ensures very efficient energy transfer to the Os complex dopants. PVK:PBD has an EL emission around 450 nm which does not overlap the absorption bands of the osmium complexes and also produces devices of lower efficiency, but PVK is a better transport layer and therefore produces brighter devices. The best external quantum efficiency, of the double-layer devices was 2.2%, with a photometric efficiency of 1.9 cd/A. The brightest device achieved was 1,600 cd/m2.

Recent progress in developing high-performance organic polymers for electro-optics and photonics is reviewed. A highly fluorinated hyperbranched aromatic polymer with the degree of branching around 0.51 was prepared by a mild one-step polyesterification of an AB2 type monomer. Further post-functionalization with and thermally cross-linking by aromatic trifluorovinyl ethers (TFVE) afforded thermally stable, low loss optical polymer with improved solvent resistance. By more precisely controlling the molecular nano-architecture, we have developed a series of highly fluorinated crosslinkable dendrimers. These materials possess most of the desirable properties needed for the fabrication of optical waveguides, such as high solubility in common organic solvents (up to 50 wt%), very low optical loss, and excellent thermal stability. To overcome the “nonlinearity-stability tradeoff,” a facile and reversibly crosslinkable NLO polymer system is developed that combines both advantages of high poling efficiency and good alignment thermal stability. By smartly controlling the poling and crosslinking processes through the reversible Diels-Alder (DA) reactions, it allows highly polarizable chromophores to be efficiently poled at the stage of low viscosity linear thermoplastic polymer. The resulting nonlinear optical polymer exhibits a combination of a very large r33 value (76 pm/V at 1.3 μm) and good temporal stability at 70°C.

Future generations of photonic devices which incorporate poled organic nonlinear optical materials may be aided by, or require the use of non-traditional electrodes. This report details the integration of highly doped silicon as one of the poling/modulating electrodes in the simple reflection type experiment for determination of nonlinear optical activity in a guest-host polymer system. The measurements illustrate that the behavior of doped-silicon and the traditional indium tin oxide (ITO) electrodes are analogous. A number of organic chromophore guests were investigated as well as multiple polymer hosts. Results demonstrate both successful poling and subsequent modulation of NLO materials, including the calculation of r33 values comparable to those achieved using a standard ITO electrode.

Highly purified deoxyribonucleic acid (DNA) was isolated from salmon and scallop sperm by an enzymatic isolation process. Characterization of the optical and electromagnetic properties of DNA suggested suitability for optical waveguide applications. One of the characteristic features of DNA we discovered was an intercalation of aromatic compounds into stacked layers within the double helix of DNA molecules. We found that various optical dyes inserted into the double helix of DNA molecules render optical waveguide films of dye-intercalated DNA suitable for active photonic devices. Our investigation includes intercalation of fluorescent dyes, photochromic dyes, nonlinear optic chromophores, two photon dyes and rare earth compounds into DNA comparing results with poly(methyl methacrylate) (PMMA) based materials.

Recent progress in developing high-performance nonlinear optical chromophores and polymers for electro-optics is reviewed. Using the single-mode focused microwave irradiation, a diversified family of 2,5-dihydrofuran derivatives has been synthesized as a new class of tunable electron acceptors. Very large r33 values (128 and 116 pm/V at 1.3 μm) have been demonstrated by doping one of the 2-dicyanomethylen-3-cyano-4,5,-dimethyl-5-trifluoromethyl-2,5-dihydrofuran (CF3-TCF)-based chromophores in poly(methyl methacrylate) (PMMA) and a high Tg polyquinoline (PQ-100), respectively. An excellent long-term temporal stability at 85°C has also been maintained in the PQ system. Two side-chain dendronized NLO polymers have been synthesized. Using a mild, simple, and generally applicable post-functionalization method, highly polarizable chromophores with dendritic modification has been covalently attached to side chains of poly(4-hydroxystryene). This approach provides the combined advantages of achieving better poling efficiency through the dendritic effect and shortening the development time required for E-O dendrimer synthesis. Systematic property comparison between these polymers and other conventional NLO polymers, such as guest-host and simple side-chain polymers, has been performed. Exceptionally high poling efficiency (a very large E-O coefficient of 97 pm/V at 1.3 μm) and good temporal stability at room temperature were dmeonstrated in this dendronized side-chain polymer system.

Utilizing guidance from quantum and statistical mechanics, the electro-optic coefficients of organic materials have been increased to values greater than 100 pm/V at telecommunication wavelengths (e.g., to 130 pm/V at 1.3 microns). Electro-optic materials now afford significant advantages in terms of bandwidth and electro-optic activity over inorganic materials such as lithium niobate. Moreover, organic materials have also been found to be quite processable permitting the fabrication, by reactive ion etching and photolithographic techniques, of 3-D active waveguide structures and integration with both VLSI semiconductor electronics and silica fiber optics. Stripline, cascaded prism, and microresonator structures have been fabricated, as have low-optical-loss coupling structures. A number of prototype devices demonstrating superior performance have been produced; however, the long-term, in-field performance of such devices still remains to be evaluated. Nevertheless, significant advances have been made in improving the thermal and photochemical stability of organic materials and in defining the mechanisms that define these stabilities (by testing under accelerated conditions). The role of nanoscale architecture in systematically improving stability of organic electro-optic materials, as well as contributing to enhanced electro-optic activity and reduced optical loss, has been clarified.

Material processing and device fabrication of many different electro-optic (EO) polymers developed at USC are reviewed. Detailed discussion is given to guest-host CLD/APCs, crosslinking perfluorocyclobutane (PFCB) polymer CX1, and thermally stable side-chain polymers CX2 and CX3. Excellent EO performance (1.4V at 1.31 μm, 2.1 V at 1.55 μm) was achieved in CLD/APC Mach-Zehnder modulators (2-cm, push-pull). CLD/APCs also possess low optical losses (1.2 dB/cm in slab waveguides and in thick core channel waveguides). However, the guest-host materials only have limited thermal stability (110-132 °C in short term, <60 °C in long term) and require special techniques in device fabrication. The crosslinking polymer CX1 was able to provide long-term stability at 85 oC when fully cured. It also has a low optical loss (comparable to CLD/APCs) before curing and decent EO coefficient when poled at 180 °C. However, after the films were poled at the crosslinking temperatures (200 °C or above), the transmissions of the waveguides and EO activity became very poor due to poling-induced chromophore degradation. By judicial molecular design of both chromophore and monomer structures to suppress thermal motion of polymer segments, we were able to realize the same or even better thermal stability in side-chain polymers CX2 and CX3. Since no curing is needed, devices can be poled at their optimal poling temperatures, and all good properties can be obtained simultaneously. Despite the excellent solubility in chlorinated solvents, these side-chain polymers are resistant to some other organic solvents or solutions such as acetone, photoresist and various UV-curable liquids.

Novel luminescent materials based on europium-cored complexes have been synthesized and incorporated into light emitting diodes using poly (N-vinyl-carbazole) and poly (vinyl naphthalene) blends as doping hosts. The complexes consists of fluorinated β-diketone ligands chelated to europium. Excitation of the ligands and efficient transfer of energy from the excited ligands to the metal core results in the emission of optically pure red light.
The ligands were designed such that they include a polycyclic aromatic compound, phenanthrene, and a second substituent to improve processibility. Phenanthrene is used to so that the ligand energy will match with the energy of the metal center. Partially fluorinated substituents were also used to help improve the efficiency and charge transfer capability of the resulting metal complex. The complex consisted of one equivalent of europium and three equivalents of the ligand. One equivalent of either 1,10-phenanthroline or 4,7-diphenyl-1,10-phenanthroline was also chelated to enhance the stability of the complex.
Double and triple layer devices were synthesized with the configuration of ITO/BTPD-PFCB/Europium complex in a polymer blend/Ca/Ag for the double layer device and ITO/BTPD-PFCB/Europium complex in a polymer blend/PBD/Ca/Ag for the triple layer device. The double layer devices made with a polymer blend of PVN outperformed the devices made from PVK as the emission bands of the PVN better match the absorption bands of the ligands. A maximum brightness of 178 cd/m2 with a maximum external quantum efficiency of 0.45% was measured for the double layer device.

In this work we present the synthesis and characterization of several novel osmium complexes of the form [Os(N-N)2L-L]2+ 2X- designed for organic light emitting device (OLED) applications. In the complex notation N-N represents a derivative of 2,2'-bipyridine or 1,10-phenanthroline and L-L represents a strong π-acid arsine or phosphine ligand. The complexes feature 3MLCT emission that ranges from 611 - 650 nm, which makes them suitable as an emission source for red OLEDs. Phosphorescent quantum yields as high as 45% and emission lifetimes as short as 400 nanoseconds have been reached.

Employing guidance from quantum and statistical mechanics, the electro-optic activity of organic materials has been increased to values greater than 100 pm/V at telecommunication wavelengths (e.g., 130 pm/V at 1.3 microns). Electro-optic materials now afford significant advantages in terms of bandwidth and electro-optic activity over competitive inorganic materials such as lithium niobate. Organic materials have also been found to be quite processable permitting the fabrication by reactive ion etching and photolithographic techniques of 3-D active waveguide structures and integration with both VLSI semiconductor electronics and silica fiber optics. Both stripline and microresonator structures have been fabricated, as have low-optical-loss coupling structures. A number of prototype devices demonstrating superior performance have been demonstrated; however, the long-term, in-field performance of such devices still remains to be evaluated. This article focuses on statistical mechanical theoretical methods that have aided the design of improved materials.

Monte Carlo simulations suggest that the functionalization of bulky side groups on highly efficient nonlinear optical chromophores will improve the poling efficiency of the electro-optic polymers by reducing the intermolecular electrostatic interactions from these large dipole moments (μ) chromophores. However, very little information has been provided from theoretical simulation to describe the optimal functionality of the bulky side group needed on individual chromophore in order to be compatible with its environment, e.g. neighboring chromophores and polymer matrix. To further understand the influence of side-chain modification of chromophore on both chromophore-chromophore and chromophore-polymer matrix interactions, we have synthesized a series of highly polarizable nonlinear optical chromophores with various side-chain modifications in terms of shape, rigidity and functionality. Linear E-O coefficients (r33) of these functionalized chromophores in amorphous poly(carbonate) were evaluated using the contact poling technique. Several important chromophore and polymer parameters, such as, steric hindrance and free volume were used to explain the overall results from chromophore-chromophore and chromophore-polymer matrix interactions on E-O property.

Recent development of dendron-containing NLO chromophores and polymers is summarized. By modifying the chromophore shape or applying the site isolation principle to these materials, we have systematically build up our understanding of how to molecular engineer the NLO materials. In this process, we have introduced the dentritic structures to these materials, varied from 3-D shaped dendritic chromophore, to fully-functionalized dendrimers with the center cores of NLO chromophores and crosslinkable periphery, and to side-chain dendronized NLO polymers. Compared to the conventional designed organic NLO materials, these nanoscale tailored NLO chromophores and macromolecules provide great opportunities for the simultaneous optimization of macroscopic electro-optic activity, thermal stability, and optical loss.

The electrochemical properties of carbon nanotube (NT) assemblies are relevant for many potential nanotube applications including super-capacitors, batteries, fuel cells and actuators. In this work, the double-layer capacitance of a paper of single-walled carbon nanotubes is determined for a series of concentrations of NaCl in water. The dependence of capacitance on potential was also determined in an effort to locate the potential of zero charge (PZC) for each NaCl concentration. The double-layer capacitance of the NT paper is seen to increase with electrolyte concentration, while the PZC (capacitance minimum) is seen to depend more on the sequence of electrolyte concentration tested (sample history) than on the concentration of electrolyte itself.

Optoelectronic devices based on nonlinear optic (NLO) polymers, with electro-optic (EO) coefficients in excess of 100 pm/V at 1.06 μm and dielectric constants of < 3, have demonstrated 100+ GHz data rates with less than 4 volt operating voltages. This has gained interest from the space based applications community, since in addition to being tolerant to a space environment, electro-optic devices for space applications will also need to operate at high data rates and at low operational powers. We have investigated various NLO polymers for core materials as well as passive polymers with various conductivities, both ionic and electronic, suitable for use as optical cladding layers in NLO polymer based opto-electronic devices. Our goal was to find materials that would be tolerant to irradiation as well as maximizing the nonlinearity of the NLO core material, thus minimizing the total applied poling voltage, and minimize the optical absorption loss. Using a cladding material that is more conductive than the NLO core material, the majority of the applied poling voltage is dropped across the core, thus maximizing the EO coefficient with minimum applied voltage or power. We found, however, that it is necessary to balance the optical and electromagnetic properties of the materials with their processability and compatibility.

Efficient red electrophosphorescence was achieved from double-layer light emitting devices using osmium (Os) complex doped blends of either poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD), or poly(vinyl naphthalene) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVN:PBD) as the emitting layer. Blending PVN with PBD greatly suppresses the electromer emission of PVN. The PVN:PBD blend emanates a short wavelength EL emission peaking at around 375 nm, which well overlaps with the absorption spectra of the Os complexes and ensures very efficient energy transfer to the Os complex dopants. PVK:PBD has and EL emission around 450 nm which does not overlap the absorption bands of the osmium complexes as well and produces devices of lower efficiency, but PVK is a better transport layer and produces brighter devices. The best external quantum efficiency of the double-layer devices was 2.2%, with a photometric efficiency of 1.9 cd/A. The brightest device achieved was 1,400 cd/m2.

Europium cored complexes may be used as a source of red emission in light emitting diodes. Novel europium cored complexes have been synthesized and incorporated into organic light emitting diodes (OLED's). These complexes emit red light at 615 nm with a full width half maximum (FWHM) of less than 5 nm.
The europium complexes consist of one equivalent of europium chelated to three equivalents of a nonsymmetrical β-diketone ligand. The Claissen condensation of a polycyclic aromatic sensitizer and an ester of a fluorinated carboxylic acid create the ligands. The use of a sensitizer such as phenanthrene results in a ligand that has an emission band that directly overlaps with the absorption band of europium. The use of fluorinated chains improves the overall processibility as well as the charge transfer capability of the resulting metal cored complex. The europium core is further encapsulated by the inclusion of an additional polycyclic aromatic compound such as 4, 7 diphenyl - 1, 10 phenanthroline. Emission of 615 nm light is accomplished through excitation of the ligand and efficient Forrester energy transfer to the europium complex.
A multiple layer device consisting of a substrate of indium tin oxide, followed by thin layers of BTPD-PFCB (with a thickness of 20nm), a polymer blend containing the europium complex (30 nm), followed by a layer of calcium (50nm) and finally a protective layer of silver (120 nm). The polymer blends were either poly(n-vinyl carbazole)(PVK) or poly vinyl naphthalene (PVN). The device performance was further improved by the incorporation of another lanthanide metal complex. These complexes were based upon similar ligands surrounding gadolinium. In these devices, there is a Dexter energy transfer as well as the Forster energy transfer. For the devices that are based on a PVN:PBD as a polymer host, the lowest turn on voltage was 12.0 volts. The devices that use PVK:TPD devices was 178 cd/m2 with an external quantum efficiency of 0.61%.For PVK:TKD the brightness was 116 cd/m2 with an external quantum efficiency of 0.048%. Devices that incorporate the gadolinium complexes have the turn on voltage of 5.6 volts. We report a maximum brightness of 201 cd/m2 with an external quantum efficiency of 1.0%.

For accurate design and modeling of nonlinear optic polymer electro-optic (EO) waveguide devices, potential materials need to be thoroughly characterized. Presented here are the properties of several state of the art materials used for nonlinear optical (NLO) polymer devices, such as Cheng Larry Dalton (CLD) based NLO polymers as well as conductive polymers and epoxies. This characterization includes refractive index, propagation loss, conductivity, nonlinearity, and low and high frequency dielectric constant measurements, as well as materials compatibility.

The Display and Beam Steering Thrust of the AFOSR Liquid Crystal MURI addressed key materials and device technology issues affecting performance of liquid crystal (LC) electro-optic (EO) devices, particularly device structures useful in information Displays and for Laser Beam Steering and Switching. Two basic themes were development of bulk LCs having high performance characteristics (nematic LCs, and chiral smectic LC devices having analog response), and development of novel LC electro-optic structures. Research on novel device structures led to advances in LC alignment and on photonic band-gap materials.

We have investigated various conductive and nonconductive polymer materials suitable for use as cladding layers in nonlinear optic (NLO) polymer based opto-electronic devices. Our goal was to maximize the nonlinearity of the NLO core materials, while minimizing the total poling voltage and minimizing the absorption loss. Using a cladding material that is more conductive than the NLO core material, the majority of the applied poling voltage is dropped across the core, realizing a maximum EO coefficient with minimum applied poling voltage. We found, however, that there are tradeoffs between absorption loss, conductivity, refractive index, materials processability and materials compatibility when using off-the-shelf materials. Results are presented for a 3-layer device structure using a conductive polymer material for both the top and bottom cladding layers.

A series of dendron-modified nonlinear optical (NLO) chromophores and multiple chromophore-containing crosslinkable NLO dendrimers have been developed. The enhancement of poling efficiency (40%) in the dendritic NLO chromophore/polymer guest/host system was obtained due to the significant minimization of intermolecular electrostatic interactions among chromophores by the dendritic effect. Multiple NLO chromophore building blocks can be further placed into a dendrimer to construct precise molecular architecture with predetermined chemical composition. The site-isolation effect, through the encapsulation of NLO moieties by dendrons, can greatly enhance the performance of electro-optic (E-O) materials. A very large E-O coefficient (r33=60 pm/V at 1.55 micrometers ) and high temporal stability (85 degree(s)C for more than 1000 h) were achieved in a NLO dendrimer developed through the double-end functionalization of a 3D shape phenyl-tetracyanobutadienyl (Ph-TCBD)- containing NLO chromophore with thermally crosslinkable trifluorovinylether-containing dendrons.

We have investigated various conductive and non-conductive polymers suitable for use as cladding layers in nonlinear optic (NLO) polymer based opto-electronic devices. Our goal was to maximize the nonlinearity of the core material, minimize the total poling voltage, and minimize the absorption loss. Using a cladding material that is more conductive than the NLO core material, the majority of the applied poling voltage is dropped across the core, realizing a maximum EO coefficient with minimum applied voltage. We found, however, that there are tradeoffs between absorption loss, conductivity, refractive index, materials processability and materials compatibility when using off-the-shelf materials.

We fabricated and demonstrated a beam deflector implemented in an electro-optic polymer planar waveguide. An array of prism- shaped electrodes formed on the top of the waveguide induces selective refractive index change in the core polymer layer, which results in the tilt of the propagation direction of the guided beam. Waveguide beam deflectors have potential applications in the emerging photonics technologies such as optical storage systems, optical phased array antenna, and optical switching. The deflection sensitivity of 28 mrad/kV, and the maximum deflection angle of +/- 8.4 mrad at +/- 300 V were obtained for this first demonstrated device.

Optimizing the performance of organic electro-optic modulator materials requires the consideration of many issues including the optimization of chromophore molecular hyperpolarizability, the effective translation of molecular electro-optic activity to macroscopic electro-optic activity, the stabilization of induced electro-optic activity, the processing of bulk materials into active buried channel waveguides of appropriate dimensions, and the integration of polymeric electro-optic circuitry with semiconductor electronics and silica fiber optics. The utilization of theoretical methods to design chromophores and optimize processing protocols is reviewed. Device performance is defined by material optical loss, thermal stability, photochemical stability, and processability as well as by electro-optic activity.

Studies on the influence of chromophore geometry on electro- optic coefficient/loading density and poling efficiency reveal that chromophore optical loading density is largely defined by the shape of the center of chromophore, and bulky groups at the end of chromophore is not preferable for most efficient poling of chromophore dipole. An EO coefficient of 122 pm/V at 1.06 micrometers has been achieved as a result of the systematic chromophore geometry optimization. Even high EO coefficients are expected to realized in the near future. Practical Mach-Zehnder modulators have been fabricated using CLD-1/APC material and have shown good dynamic thermal stability (120 degree(s)C), low optical loss (1.67db?cm at 1.55 micrometers ), low modulation voltage (2.4 volt, 2cm modulation length), and high extinction ratio (26dB).

The rapid development of ultra-wide bandwidth fiber optical communications networks has challenged circuit designers to obtain ever-increasing link gain-bandwidth products with new electro-optic modulators. As the link bandwidth increases, high power modulator drivers become very costly and have low efficiency. To overcome the limited gain-bandwidth product, it is important to reduce the required driving voltage or the so-called halfwave voltage of current electro-optic modulators. In this paper, we report results on new polymeric electro-optic modulators with a halfwave voltage of 0.8V and a halfwave voltage-interaction length product of 2.2V-cm. The low driving voltage allows electro-optic modulators to be driven directly by high-speed logic circuits without an amplifier. The driving electronics and the system cost can be significantly reduced when these modulators are implemented. Here, low halfwave voltage modulators are based on recent developments in materials and modulator fabrication technologies. The incorporation of a new second-order nonlinear optical chromophore CLD-1 in a poly(methylmethacrylate) matrix has a demonstrated electrooptic coefficient approximately 60 pm/V at 1318 nm wavelength. Using this material system and an optical push- pull modulator design, sub-1 volt Mach Zehnder modulators and temporal stability of these modulators will be reported.

Photonic time-stretch has been proposed as a signal preprocessor to perform A/D conversion in otherwise inaccessible high frequency regimes. We have demonstrated time-stretching of MM-wave signals at frequencies up to 102 GHz down to 11 GHz , using an electrooptic modulator fabricated with the new polymer material PC-CLD. This application takes advantage of the inherent wideband capabilities of the PC-CLD material system, which has also demonstrated good optical insertion loss and high non- linearity at 1.55 micrometers . The dispersion penalty inherent to time-stretching imposes an additional bandwidth limit to that imposed by the modulator. A single-sideband modulator configuration is proposed to reduced the effect of this penalty.

Chromophore-containing polymeric electro-optic materials must satisfy many requirements before they can be considered for use in applications at telecommunication wavelengths (1.3 and 1.55 microns). These include large macroscopic electro-optic activity, low optical loss, and stability (thermal, chemical, and photochemical). Such materials must be capable of being integrated with silica fiber optics and semiconductor electronics. We discuss design of chromophores not only for large hyperpolarizability but also for low optical loss and for thermal and photochemical stability. The processing of these materials to maximize electro-optic activity while minimizing processing- associated optical loss is discussed. Device structures appropriate for minimizing insertion loss are discussed, as is the fabrication of such dvices and three-dimensional active/passive optical circuits. The identification of new structure/function relationships provide design criteria for future improvements as well as permitting better definition of the performance limitations that can be expected for polymeric electro-optic materials prepared by electric field poling methods.

We have demonstrated an enhancement in the effective electro-optic (EO) coefficient of electrode poled nonlinear optical polymers using a conductive polymer cladding. We have also demonstrated the lowest poling voltage to date, 300 V, for a 2 micrometers thick NLO polymer core and 2 micrometers thick conductive polymer cladding structure asymmetric waveguide structure. With the cladding material more conductive than the core material, the majority of the applied poling voltage is dropped across the core, maximizing poling efficiency and, hence, realizing a higher EO coefficient. These results show promise for lower operating voltage devices.

A beam deflector device has been demonstrated that used thin-film electro-optical polymeric waveguide. Prism cascade was fabricated within a planar waveguide. We report the detail of the design and fabrication of new polymer material beam deflector to operate at 1.3 micrometers .

We have demonstrated a polymeric electro-optic modulator based on a 1 X 2 Y-fed directional waveguide coupler. The symmetric geometry of the 1 X 2 Y-fed directional coupler provided the modulator unique characteristics of intrinsic 3 dB operating point and two complementary output ends. A low switching voltage of 3.6 V and a high extinction ratio of 26 dB were obtained with the modulator operating at a wavelength of 1.34 micrometers . The modulator was fabricated with a novel electro-optic polymer that was synthesized from polyurethane crosslinking with a chromophore.

Presented is the effect of using various cladding layers with different dielectric constants on the applied modulation voltage for nonlinear optic (NLO) polymer based integrated OE devices. The dielectric constants of the core and cladding materials used for NLOs polymer based integrated optoelectronic devices are typically very similar in magnitude. This suggests that even for low modulation rates, only 20% to 25% of the applied modulation voltage (voltage between the electrodes) is being dropped across the core region. With this small percentage of applied voltage reaching the NLO core layer, it becomes necessary to apply 4 to 5 times higher modulation voltage in order to achieve the desired (pi) phase change through the core.

A new series of highly efficient, chemically and thermally stable nonlinear optical chromophores have been developed by using a 2-phenyl-tetracyanovinylbutadienyl group as the electron acceptor for a series of dialkyl- or diphenyl-amino substituted thiophene stilbenes. Excellent tradeoffs among absorption, molecular nonlinearity and thermal stability were achieved. Electro-optic polymers based on the guest/host systems and covalent attachment of chromophores onto high temperature polyquinoline backbones demonstrate high E-O activities and good optical, electrical and mechanical properties.

We present design and fabrication considerations for a vertically integrated electro-optic polymer modulator. The hybrid design incorporates both passive and active core segments for optimized transmission and modulation of an optical signal. When compared to traditional structures, this vertically integrated modulator potentially reduces fiber coupling and propagation losses by more than 10 dB for a 6 cm structure while maintaining a minimized V(pi ).

The nonlinear optical properties of N,N-diphenyl-7-[2-(4- pyridinyl) ethenyl]-9,9-di-n-decylfluoren-2-amine [AF- 50] have been investigated. The nonlinear absorption of a saturated solution of this material in acetone was investigated with 430 femtosecond pulses at 790 nm. From these results, the two-photon absorption cross-section was determined to be 25 X 10-50 cm4sec/photon molecule. This number is in agreement (within a factor of 2) with theoretical calculations. Nonlinear absorption and optical limiting measurements were also made using a Nd:YAG pumped dye laser with 4.3 ns pulses at 694 nm. These results suggest inherent differences in the performance of two-photon absorbing materials in these two different geometries.

The full potential of second order nonlinear polymers can be utilized in electro-optic polymer modulators with a DC biased operation scheme to greatly reduce the V(pi ). This technique makes use of the total achievable electro-optic coefficient, which can be more than three times as high as the residual value after the fast partial relaxation following corona or contact poling. As the result of the DC bias and with high (mu) (beta) chromophores, a low V(pi ) of 1.5 V was achieved with 2 cm long birefringent waveguide modulators at the wavelength of 1.3 micrometer. Results of 200 degrees Celsius stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the stability required for high temperature hermetic sealing because the polymer does not need to be poled before device packaging.

We present design considerations and fabrication results for a vertically integrated waveguide polarization splitter. Fabrication techniques of shadow reactive ion etching (RIE) and variable photolithography exposure produced the required vertical waveguide structures. The fabricated vertical waveguide bends exhibit excess loss of only 0.2dB. By constructing this vertical bend with a birefringent polyimide, simulation results show the possibility of a polarization splitter with an extinction ratio of over 15dB. We demonstrate preliminary waveguide experiments showing the practicality of these structures as three dimensionally integrated optical devices.

We present new femtosecond degenerate four-wave (DFWM) measurements on a C70 film in the wavelength range 0.9- 1.6 micrometers in conjunction with previously measured data in C60 and C70 in the ranges 0.74-1.7 (mu) and 0.74-0.88 micrometers , respectively. The new data reveal tow closely spaced peaks in the DFWM spectrum which we interpret as two-photon states with excitation energies of 2.41 +/- 0.05 eV and 2.64 +/- 0.03 eV. We relate these results to nonlinear optical spectra obtained by others in C60 and C70 films. In particular, we compare third-harmonic generation, electro-absorption and DFWM and emphasize the relative advantages of DFWM for two-photon spectroscopy.

We present a novel post-fabrication laser trimming technique to adjust the power splitting ratio of strip waveguide Y-branches made in thermally crosslinked electro-optic polymers. The trimming is based on the irreversible index change due to photobleaching. Our method uses simple equipment and the process takes only a few seconds. Waveguides made by both reactive ion etching and photobleaching are trimmable. An adjustable range of the splitting ratio as wide as is achieved with less than 0.2 dB of excess loss. This in situ trimming technique is effective for both the TE and TM modes of the waveguide and is very suitable for automated device processing.

Until recently, the product of chromophore dipole moment, β, and molecular first hyperpolarizability, p, divided by chromophore molecular weight was considered to be an appropriate chromophore figure of merit. Substantial progress has been made designing and synthesizing chromophores characterized by large μβ values. If such high pp chromophores could be translated to hardened acentric polymer lattices with the same efficiency achieved for disperse red (azobenzene) chromophores then optical nonlinearities in excess of 50 pm/V could be expected. Although high μβ chromophores have been available for several years, such macroscopic optical nonlinearities have only beat recently realized. We demonstrated that the problem of translating microscopic to macroscopic optical nonlinearity can be traced to the attenuation of electric field polinginduced order by chromophore-chromophore electrostatic interactions. Such interactions are frequently treated within the approximations of London theory. We extend theoretical analysis to take into account the size and shapes of chromophores; such theory permits essentially quantitative prediction of variation of electro-optic coefficient with chromophore loading. Theory also suggests structural modification of chromophores to improve the maximum realizable optical nonlinearity as a function of chromophore loading and theoretical predictions have been experimentally realized in a number of cases leading to doubling and tripling of previously realized maximum electro-optic coefficient values. Chromophore-chromophore electrostatic interactions also contribute to aggregation and phase-separation which result in unacceptably high values of optical loss. Such interactions can also inhibit lattice hardening (e.g., thermosetting) reactions. A systematic analysis of such effects is presented.

We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling between channel waveguides and single-m,ode fibers. The taper smoothly converts a highly elliptical waveguide mode into a bigger and more circular mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5-2 mm in length is made in the low index upper cladding to reduce its thickness from several micrometers to zero, followed by the coating of a second upper cladding with index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows bigger a light propagates, whereas the confinement by the lower cladding and lateral confinement are hardly affected. The waveguide mode grows in the vertical direction away from the lossy ground electrode and substrate; therefore no compromise between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and tapered photoresist etching mask, are develop for making this vertical taper. Mode expansion and a 1.8 dB reduction in coupling los, which is not sensitive to waveguide width and polarization, is obtained in our preliminary experiment.

We have successfully characterized our ultra-fast, traveling wave modulators made from stable nonlinear electro-optic polymer materials with response over 110 GHz. The modulation as a function of frequency was directly observed using a laser heterodyne system. Major advances have also been made in other key figures of merit, systems integration, and in developing practical commercial prototypes.

We have extended the wavelength range of our previous study of the third order nonlinear optical susceptibility tensor (chi) (3)(-(omega) , (omega) , (omega) , -(omega) ) of a thin C60 film to 1.7 micrometers . We use time-resolved degenerate four-wave-mixing with femtosecond pulses to measure both the phase and magnitude of (chi) 1111. Our data are well defined in terms of a single two-photon resonance at a fundamental wavelength of 930 nm. From our fit parameters, we predict for (chi) 1111 in the zero-frequency limit a value of (9 +/- 3) X 10-13 esu and at the resonance maximum a value of i(3.9 +/- 0.6) X 10-12 esu.

We use time resolved degenerate four-wave-mixing with femtosecond pulses to measure magnitude, phase, and dispersion of all nonzero components of the third order nonlinear optical susceptibility tensor (chi) (3)(-(omega) ; (omega) , (omega) , -(omega) ) of a polycrystalline C70 film. Rise and fall times of the nonlinearities measured are short compared to the (112 plus or minus 5 fs) pulses employed. Accordingly, the cw symmetry relation (chi 1111) equals 2 (chi 1212) plus (chi 1221) is experimentally found to be satisfied. The magnitude of (chi 1221) is measured to be (5.04 plus or minus 0.19) 10-13 esu relative to fused silica independent of wavelength. The ratio (chi 1212)/(chi 1221) is wavelength dependent and varies between 1.87 plus or minus 0.12 and 1.44 plus or minus 0.09. The magnitudes of phase angles for (chi 1111) and (chi 1212) are (120 plus or minus 22) degree(s) and (105 plus or minus 21) degree(s), respectively. The intensity dependence of the observed signals is cubic for intensities up to 20 GW/cm2 at all wavelengths. Good agreement between data derived from degenerate four-wave-mixing and third-harmonic generation in C70 as well as in C60 films is found.

To demonstrate the feasibility of integrating polymer electro-optic devices on Si circuitry, we have vertically integrated a demonstration slab phase modulator on nonplanar VLSI circuitry. Optical loss measurements for waveguides fabricated on planarized circuits demonstrate that more practical devices like channel phase and Mach-Zehnder amplitude modulators can easily be integrated onto the circuits.

A novel measurement technique for characterizing both the real and imaginary parts of the electro-optic r33 and r13 coefficients of in-plane poled polymer thin films is proposed and demonstrated. Efficient in plane poling with applied DC fields up to 200 V/micrometers was achieved. A r33 of 12.5 pm/V at the 1.3 micrometers wavelength was measured for a polyurethane disperse red 19 polymer. 'Push-pull' modulation was demonstrated.

A major requirement for polymeric electro-optic materials is that they must possess noncentrosymmetric (roughly uniaxial) order of chromophores in the bulk material. Thermodynamic relaxation of this chromophore alignment is prevented by raising the glass- transition temperature of the polymeric materials during the electric-field poling process. This is accomplished by (1) thermal imidization of a poly(amic acid) prepolymer, (2) thermally induced chemical crosslinking of an acrylate-type prepolymer, prepared from chromophores containing differing reactive functionalities, (3) sol-gel processing of alkoxysilane- incorporated chromophores, and (4) thermosetting polyurethane/polyurea materials. Analogs of these chromophores that contain reversible photoactive moieties are attached to the surface of functionalized polystyrene and polyacrolein beads permitting the realization of room temperature persistent spectral hole burning exploiting morphology-dependent resonances. Such resonances provide the basis of wavelength coding for the development of three and four-dimensional high-density optical memories.

We measure the magnitude and phase of both independent components of the femtosecond (fs) third-order nonlinear optical susceptibility tensor (chi) (3)(-(omega) ;(omega) ,(omega) ,-(omega) ) of a C60 film. We observe only the contribution of mechanisms whose rise and decay times are short compared to our 120 fs microjoule pulses. The value of (chi) 1111 varies between (6.39 +/- 0.35) X 10-13 esu at 745 nm and (19.7 +/- 1.1) X 10-13 esu at 875 nm, relative to fused silica, and rises monotonically with wavelength. Its phase angles lie between 100 and 150 degrees. Our results indicate that neither our, nor any previously published, measurements can be assumed to have approached the low frequency limit in C60.

We have developed two classes of highly efficient and thermally stable nonlinear optical chromophores using fused-thiophene and bithiophene as conjugating units. Experimental studies indicate that the use of fused-thiophene or bithiophene as a (pi) conjugating bridge provides an excellent tradeoff between nonlinearity and thermal stability. In addition to the chromophore developments, we have employed new synthetic methodologies to obtain thermally stable poled polyimides.

A simple and easy method to study the dispersion of electro-optic coefficients of poled second- order nonlinear optical polymer films is presented. Phase grating type electro-optic modulators were used to measure the relative electro-optic effects at different wavelengths. The grating structures were formed by either etching a grating in the nonlinear polymer thin films or defining a transparent electrode on top of a uniform polymer film. When an AC voltage is applied to the electrodes, the diffraction efficiency of the grating is modulated by the small index modulation. The measurement of the electro-optic response can be carried over a large wavelength range, even deep into the absorption band of the material due to the short interaction length of the optical beam and the polymer thin film. The grating modulation method uses a single optical beam in a transmission arrangement which requires little optical alignment and no polarization optics. With a properly designed electrode, the grating modulator can also be used in measuring the electro-optic coefficient, r13, of the poled polymer films. Other measurement applications such as monitoring temporal, thermal, and photo-excitation stability are discussed.

We measure the magnitude and phase of the degenerate third-order nonlinear optical susceptibility (chi) (3)llll of solutions of various bis-thienyl polyenes (n-BTP) with the number n of the conjugated double bonds ranging from 3 to 9. We study both neutral and bipolaronic (i.e., doubly ionized) forms of n-BTP. We find that, within experimental error, (chi) (3)llll is proportional to nb where b-5.5 at 532 nm for our neutral n-BTP samples which have 3 <EQ n <EQ 9, and b-14 at 1.06 micrometers for the bipolaron state samples which have 6 <EQ n <EQ 9 where the probing laser wavelength is close to an absorption band. We calculate (chi) (3)llll of the bipolaronic n-BTP assuming it is associated with this absorption band acting as a two-level system and find good agreement with experiment.

We report our study of a new sol-gel polymer for nonlinear optics applications. An amino- sulfone dye chromophore was covalently incorporated into a sol-gel network and each chromophore was firmly anchored at both ends via nine possible crosslinking sites. After corona poling and thermal curing at elevated temperatures using a new kind of `step' poling profile, a d33 of 27 pm/V was measured at the 1.06 micrometers fundamental wavelength. Long term stability at 100 degree(s)C and short term stability at 200 degree(s)C were demonstrated. A phenomenological explanation for the behavior of the dynamic SHG signal to our `step' profile is also proposed.

We have developed several classes of thermally stable nonlinear optical chromophores based on the combination of efficient thiophene conjugating units and novel electron-donating and electron-accepting functional groups. The incorporation of these chromophores into high temperature polymers produces high linear electro-optic coefficients and long-term thermal stability at elevated temperatures. Active Mach-Zehnder interferometers with a V(pi) phase shift of 50 volts and low attenuation (< 2 dB/cm) were fabricated. Thermal baking of the poled device demonstrated no change in activity after 30 minutes at 230 degree(s)C.

A number of new thermally crosslinkable second-order nonlinear optical polymers have been developed and characterized. These polymers are designed for stable nonlinear optical activities since both ends of the rod-like chromophores are locked into a polymer matrix by covalent bonds. Sizable nonlinearities were measured in these polymers and the thermal stability of both main chain and side chain polymers were improved significantly by thermally induced crosslinking. These thermosetting polymers, with the chromophores either included in the main chain or as side chain pendants, have been used in a number of device applications. Waveguide structures can be defined in these polymers by reactive ion etching or ultraviolet bleaching. Thin film integrated optical devices, such as high frequency electro-optic modulators and birefringent directional couplers have been fabricated with reactive ion etching and photo bleaching methods. Waveguide fabrication techniques for multi-layer structures are discussed in detail.

We report our study of a second-order nonlinear optical polymer in which the chromophores were first attached at one end to the polymer backbone as side chains and then crosslinked at the other end during electric field poling and thermal curing. The corona poled polymer films showed a sizable second-harmonic generation coefficient d33 of 60 pm/V at 1.064 micrometers fundamental wavelength. The cured polymer film showed long-term stable nonlinearity from room temperature to 90 $DEGC. Improved thermal stability at 125 $DEGC was also obtained. A simple and quick method for measuring the short-term thermal stability of nonlinearity is presented.

Ultrastructure synthesis techniques for stabilization of large second order optical nonlinearities of poled polymers are reviewed. These techniques include covalent attachment of chromophores onto polyimide backbones, use of double-end crosslinkable chromophores, crosslinking of main-chain polymers with chromophores as polymer backbone components, and in-situ poling and polymerization of chromophores with multiple functionalities. By using these techniques, second harmonic generation coefficients, measured at 1064 nm wavelength, on the order of 10-7 esu and long term stability of optical nonlinearity at 90 - 125$DEGC have been realized.

We have developed a new class of main-chain second-order nonlinear optical (NLO) polymers using well-developed condensation polymerization methods. In these polymers, the NLO chromophore dipoles are expected to be randomly arranged along the polymer backbone (i.e., the dipoles can be head-to-tail, head-to-head, or tail-to-tail). For comparison, a side-chain polymer having virtually the same chromophore as a pendant has also been prepared. The effect of variation in polymer structure on the second-order NLO properties and the effect of crosslinking on the stability of poling-induced macroscopic order are studied. Our results demonstrate that the random main-chain, second-order NLO polymers can be efficiently poled, yielding (chi) (2) as high as 300 pm/V. Long-term temporal stability of the poling- induced order (e.g., no significant NLO decay is observed for more than 2000 hours) can be realized by crosslinking the polymer backbone.

The nonlinear and linear optical properties of a group of polymers containing DR19 are reviewed. The thermal setting polymers have demonstrated large NLO coefficient and long term poling stability. Dry processed micro-patterning of the index of refraction and the birefringence has been demonstrated with sub-micron resolution.

Optical nonlinearities can arise as the result of intense electromagnetic radiation fields inducing either changes in electron or nuclear configurations. Indeed, as is discussed in this paper, several mechanisms, including mechanisms depending upon electron-phonon coupling, may be elicited from the same material. The precise contribution that a given mechanism makes to observed optical nonlinearity is often dependent upon pulse conditions employed in transient nonlinear optical experiments. The ability to control optical nonlinearity by pulse conditions is demonstrated and analyzed for a high symmetry ladder polymer where contributions from coherent parametric mixing, excitons, and bipolarons are observed. The different timescales associated with various mechanisms for index of refraction and absorption changes are discussed. The utilization of photo-induced changes occurring on widely different timescales is demonstrated in the realization of efficient second harmonic generation by quasi- phase matching. The role of chemical synthesis in engineering multi-functional materials is discussed.

Multifunctional properties of nonlinear optical chromophores are discussed both in terms of a given chromophore exhibiting more than one type or mechanism of optical nonlinearity and in terms of a chromophore exhibiting useful auxiliary properties. For materials exhibiting more than one type of mechanism of optical nonlinearity, the concept of pulse-controlled optical nonlinearity is introduced and discussed. An analogy is drawn to multidimensional nuclear magnetic resonance studies which are useful in systematically elucidating excited state dynamics. Practically, pulsed control of optical nonlinearity provides a means of enhancing and modulating nonlinear optical phenomena. The photochemical reactivity of nonlinear optical chromophores is discussed in terms of fabricating ordered lattices appropriate for the development of integrated circuits and the realization of specific effects such as quasi-phase matching in second harmonic generation.

This paper presents the study of the photoinduced refractive index change and birefringence in a nonlinear optical polymer --polyester with disperse red 19 side groups. Polyester with disperse red 19 side groups showed sizable second-order nonlinear optical properties when poled under intense electric field. In addition, under ultra-violet or short wavelength visible light illumination, large photoinduced refractive index changes were measured in the near infrared region. Furthermore, with linearly polarized light illumination large photoinduced birefringence was also exhibited in the thin films of this polymer. Some device structures, such as birefringent gratings, thin film waveplates, and optical waveguides, were generated by photo exposure method. A simple theoretical model is also presented to investigate the relation between the photoinduced birefringence and the refractive index change.

Several electroactive polymers, such as polyacetylene, polythiophene, poly [p-phenylene vinylene] and poly [2,5-thienylene vinylene] have shown promise as NLO-active materials over the past few years. However, as several theoretical and experimental research groups have pointed out in recent publications and symposia, it is not evident that long conjugation lengths are necessary for enhanced (chi) (3) activity. As recently demonstrated, copolyamides which incorporate polyenylic or PTV oligomeric repeat units show (chi) (3)/(alpha) values of ca. 10-13 esu-cm at 532 nm(band-edge). In this paper, the authors discuss how ladder subunits related to the electroactive polymers POL and PTL can be incorporated into polymer films as (a) copolymer repeat units, (b) pendant groups attached to poly [p-hydroxystyrene] and (c) guest-host composites in polycarbonate. Sharp optical absorptions are found in all cases as well as promising (chi) (3) properties.

Second order nonlinear optical (NLO) polymers containing NLO moieties with large optical nonlinearities and a cross-linkable unit have been synthesized using difunctionalized disperse red dye. The enhanced second order NLO coefficients, X exp (2) of 250 pm/v for the first polymer and 500 pm/v for the second, were obtained at 532 nm using the corona poling method. The introduction of flexible chains into the polymer backbone is found to cause a decrease in glass transition temperature and, hence, a decrease in the stability of the second-order NLO effects.

During the past three years it has become more evident that long conjugation sequences in electroactive materials may
not be a stringent requirement for high third order nonlinear optical (NLO) activity. Since long conjugation lengths in these
materials often make them difficult to process, the resulting insolubility often precludes the formation of optical quality films
for device applications. The incorporation of shorter electroactive segments alternating with flexible non-active spacers may
allow high NLO activity coupled with good optical film forming capability. In this paper we would like to present several
approaches to copolymer design which incorporate various electroactive oligomer segments with well-defined conjugation
lengths. The control one obtains in this appmach allows the design of sharp optical windows, and the ability to tailor
absorption characteristics to particular frequencies.

Third order nonlinear optical properties of organic ladder copolymer (POL) system is studied
using degenerate four-wave mixing with picosecond laser pulse. Both the real and imaginary part
of the third order nonlinear susceptibility (3) were determined by a new phase conjugate
interferometric method over the wavelength range of 532 - 720 nm. From the space symmetry and
wavelength dependence of -) we attribute the observed nonlinearity to the nonlinear
photoexcitation of bipolarion states in this ladder copolymer system.

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